John Isner and Fabio Fognini continued their pushes to reach the ATP Finals after moving into the Stockholm Open last four on Friday.
Isner needed almost three hours to get past fellow American Tennys Sandgren 7-6 (10-8) 6-7 (5-7) 7-6 (7-2) in the quarter-finals of the ATP 250 event.
The top seed is on track to secure one of the three remaining spots for the showpiece event in London next month.
Fognini remains a chance of qualifying for the tournament, the Italian reaching the last four after South Korean Chung Hyeon retired when trailing 7-5 2-1.
Ernests Gulbis, Isner's next opponent, upset Jack Sock 4-6 6-3 6-4, while Stefanos Tsitsipas was a 6-3 7-6 (7-4) winner against Philipp Kohlschreiber.
Richard Gasquet survived a huge scare to reach the European Open semi-finals, while an all-Russian last-four clash was set up in Moscow.
Gasquet, the fourth seed in Antwerp, saved a match point before edging past Jan-Lennard Struff 6-4 6-7 (4-7) 7-6 (11-9) in their quarter-final on Friday.
While the Frenchman battled, his last-four opponent – Kyle Edmund – received a walkover against qualifier Ilya Ivashka.
The other semi-final will see Gael Monfils face Diego Schwartzman after both recorded straight-sets wins.
Monfils was too good for Vasek Pospisil 7-5 6-4 and Schwartzman cruised past Gilles Simon 6-4 6-3.
At the Kremlin Cup, Daniil Medvedev and Karen Khachanov moved into an all-Russian semi-final.
Medvedev, the second seed, overcame lucky loser Ricardas Berankis 6-2 1-6 6-4, while third seed Khachanov beat Mirza Basic 6-2 7-6 (7-5).
